Method of producing high strength elongated products containing nanotubes

ABSTRACT

The present invention relates to a method of producing a high strength and high modulus elongated product comprising the steps of (a) making a composition comprising a semi-crystalline polymer and carbon nanotubes, (b) extruding said composition into an elongated product, and (c) stretching the product below the melting point of the polymer, wherein in step (a) the composition is a colloidal dispersion of nanotubes in a solution of the polymer. The advantages of the invention include production of elongated products, like fibers with higher tensile properties, especially strength, with a lower concentration of nanotubes than with a known method. The invention also concerns a high strength elongated product containing nanotubes obtainable by the method according to the invention, especially a polyolefin fiber containing nanotubes having a tensile strength of higher than 3.0 GPa. The invention also relates to a process for making composite articles wherein high strength elongated products, preferably fibers, according to the invention are used and to anti-ballistic composites comprising said products.

CROSS REFERENCE TO RELATED APPLICATION

This application is the National Phase of International ApplicationPCT/NL03/00083 filed Feb. 7, 2003 which designated the U.S., and waspublished in the English language.

The invention relates to a method of producing an elongated productcomprising the steps of (a) making a composition comprising asemi-crystalline polymer and nanotubes, (b) extruding said compositioninto an elongated product, and (c) stretching the product below themelting point of the polymer. The invention further relates to a highstrength elongated product containing nanotubes obtainable by the methodaccording to the invention, especially a polyolefin fibre containingnanotubes having a tensile strength of higher than 3.0 GPa. Theinvention also concerns a process for making composite articles whereinhigh strength elongated products, preferably fibres, according to theinvention are used, and anti-ballistic composites comprising saidelongated products.

Such a method is known from WO 00/69958 A1. In this patent application amethod is described wherein in step (a) carbon nanotubes are introducedinto a semi-crystalline polymer, i.c. isotactic polypropylene (iPP), viamelt compounding, which composition is then melt extruded in step (b)into fibres, and in step (c) stretched in the solid state so as toorient the carbon nanotubes. It is reported that iPP fibres can be madewith a tensile strength of up to about 2.3 GPa and a tensile modulus (at1% strain) of up to about 21 GPa. The maximum solid-state stretch ratiothat could be applied is indicated to be 6.3.

Within the context of this application an elongated product isunderstood to be any elongated product having a dimension in at leastone direction that is much larger than in at least one of the otherdirections. Examples of such elongated products include fibres orfilaments, tapes, ribbons, films, and sheets.

Carbon nanotubes, hereinafter also referred to as nanotubes, arecarbon-based molecules having a structure related to the structure ofso-called Buckminsterfullerene (C₆₀) and other fullerenes. Nanotubeshave a cylindrical structure and may grow into nearly endless tubes offrom 50 nm up to 10 mm in length. The nanotube diameter may be fromabout 0.5-100 nm. Nanotubes are presently typically made from carbon,but also other atoms may be present. Nanotubes from other atoms likesilicon, nitrogen, boron or mixtures thereof are also reported.Nanotubes would also be an ideal reinforcing fibre for polymercomposites, because they have a very high aspect ratio(length-to-diameter ratio), but are still short enough to show enoughflowability when incorporated into a polymer matrix. Nanotubes can haveonly a single-wall structure (single-wall nanotubes, abbreviated asSWNT), a double-wall structure (DWNT) or a multi-wall structure (MWNT),resembling concentric cylinders of several layers. Nanotubes show astrong tendency to form aggregates of up to 1000 nanotubes, for examplein the form of branched clusters of roughly parallel arranged tubes,inter-connected via individual nanotubes that extend into differentclusters. Such aggregates, also referred to as ropes can agglomerate toform a powder or a sheet material. Nanotubes are generally difficult todisperse in organic solvents, because of strong particle interaction inaggregates. Preparation of nanotubes, especially SWNT, and theirproperties and potential applications have been subject of numerouspublications, see for example WO 97/09272 A1 and WO 98/39250 A1.

A disadvantage of the method as described in WO 00/69958 A1 is that thetensile properties of the iPP/nanotubes fibre that is obtained are stillnot at the level desired for the most demanding applications, likeadvanced structural composites or anti-ballistic clothing.

The object of the present invention is to provide a method for producingan elongated product comprising a semi-crystalline polymer and carbonnanotubes, which product shows tensile strength significantly higherthan can be obtained by the known method.

This object is achieved according to the invention with a methodcomprising said steps (a)-(c) wherein in step (a) the composition is acolloidal dispersion of nanotubes in a solution of the polymer.

A further advantage of the method according to the invention is that alower concentration of the expensive nanotubes material can be used toobtain a certain increase in properties. On the other hand, the methodallows a higher amount of nanotubes to be dispersed into a polymermatrix and to contribute to strength increase, than would be possiblevia conventional melt mixing.

From EP 0055001 A1 it is known that a polyethylene fibre containingfiller particles can be made via a solution spinning process, but thispublication does not disclose or suggest to use nanotubes, nor acolloidal dispersion of particles as in the method of the presentinvention. In addition, the tensile strength of fibres reported thereindoes not exceed a level of 2.0 GPa.

Within the context of the present application a colloidal dispersion ofnanotubes is understood to be a dispersion of nanotubes in a suitablesolvent, wherein the nanotubes are dispersed at least as a mixture ofindividual nanotubes and aggregates of small particle size. Suchcolloidal dispersion for example does not show visual sedimentationafter at least 10 minutes without stirring. The average particle size ofaggregates in such dispersion is generally smaller than 250 nm,preferably smaller than 200 nm, more preferably smaller than 150 nm,even more preferably smaller than 100 nm, still more preferably smallerthan 50 nm, and most preferably smaller than 25 nm. With averageparticle size is meant the average apparent diameter as observed withmicroscopy of the cross-section of aggregated nanotubes particles. Withoptical microscopy normally no particles can be seen in a sample of sucha colloidal dispersion. In order to improve dispersability, thenanotubes preferably have an average length of the tube that is smallerthan 20 micron, more preferably smaller than 5 micron, still morepreferably smaller than 3 micron, even more preferably smaller than 1000nm, or even smaller than 500 nm. The advantages of making a dispersionof aggregates of ever smaller size, is that the nanotubes can also bebetter dispersed in the polymer matrix, which can result in a moreeffective contribution of the nanotubes to the mechanical strength ofthe composite fibre. The length of nanotubes should, however, not be tooshort, since a high aspect ratio contributes more to a high strength ofthe final composition. Preferably, the nanotubes show an aspect ratio ofat least 100, more preferably at least 250, even more preferably atleast 500, still more preferably at least 1000 and most preferably atleast 2000. In WO 98/39250 A1 several ways are described to adjust thelength of nanotubes in a controlled way.

In the method according to the invention preferably carbon nanotubes areused, because of their combination of properties and emergingavailability.

Preferably, single-wall nanotubes (SWNT) are used, because theycontribute more effectively to the mechanical strength of a compositeper volume fraction of nanotubes than MWNT.

The semicrystalline polymer that can be used in the method according tothe invention may be selected from a broad range of polymers.Semi-crystalline is herein understood to mean that the polymer moleculesshow local ordening, affecting the reological and/or mechanicalproperties of the polymer, and which ordening is disrupted upon heatingat a certain temperature; i.e. the melting temperature (T_(m)).Preferably a polymer is used that shows significant molecularorientation upon stretching or elongating a composition or solutioncomprising said polymer. Suitable polymers include polyamides,polyesters, polyketones, polyoxazoles, polyimidazoles, polyvinyls, andpolyolefines. Since solution spinning of a polymer is generally moreexpensive than melt spinning in view of the large amounts of solventsthat need to be used and recovered, the method according to theinvention preferably uses a semi-crystalline polymer that can not beprocessed via melt spinning, because of too high a melting point or toohigh viscosity, or a polymer that can be better oriented and elongatedduring solution spinning, resulting in higher strength. Examples of suchpolymers include aromatic polyamides, like poly(para-phenyleneterephthalamide); polybenzoxazoles or polybenzothiazoles, likepoly(p-phenylene-2,6-benzobisoxazole); polyvinyls, likepolyvinylalcohol, polyacrylonitril, or copolymers thereof; aliphaticpolyketones; and polyolefines, preferably of high molar mass, likepolypropylenes and polyethylenes. Solution spinning is also preferredfor making fibres from precursor polymers that react during spinning,likepoly(2,6-diimidazo[4,5-b4′,5′-e]pyridinylene-1,4(2,5-dihydroxy)phenylene).

In general, a process for extruding an elongated product from a polymersolution, also called a solution spinning process, can comprise one ormore of the following steps: making of a polymer solution; spinning ofthe solution into a elongated product; stretching of the product in itsfluid state (also called solution stretching); solidifying the productby cooling in air or by quenching in a non-solvent; stretching of thesolvent-containing solidified product below the melting point (T_(m)) ofthe polymer (also called gel stretching); at least partially removingthe solvent; stretching the resulting solid product, optionally athigher temperature but still below T_(m) (solid state stretching); andremoving residual solvent/non-solvent. The melting point (T_(m)) isunderstood to be the melting point of the polymer as such, determined bythermal analysis, e.g. the peak-melting temperature found by DSCanalysis (following a standard procedure as in ISO 3146). Solutionspinning of an aromatic polyamide is described in e.g. EP 0939148 A1, ofa polybenzoxazole in e.g. EP 0775222 A1. A process for solution or gelspinning of high molar mass polyethylene fibres is described in moredetail in WO 01/73173 A1. Depending on the specific polymer and solventused, above indicated steps may also take place more or lesssimultaneously.

In case of polymers with a highly rigid molecular chain structure,polymer solutions thereof may show lyotropic or (semi) liquidcrystalline behaviour, such as for poly(p-phenylene terephthalamide).Substantial molecular orientation is than generally already achievedduring spinning and solution stretching; during these stretching stepsthe temperature is normally below T_(m) of the polymer.

In a preferred embodiment according to the invention the solventnormally used for solution spinning of the polymer is also a suitablesolvent for making a colloidal dispersion of nanotubes. Highly polarpolymers are often also very difficult to dissolve because of their highcrystallinity, and solvent systems like highly concentrated strong acidsare used for solution spinning. Preferably, such solvents, like forexample fuming sulphuric acid or oleum that is used in spinning aromaticpolyamides, are used for making a colloidal dispersion of nanotubes.

In another embodiment of the method according to the inventioncomprising said steps (a)-(c), the composition of step (a) is obtainedby mixing

-   -   (a1) a colloidal dispersion of nanotubes and optionally other        components in a solvent 1; and    -   (a2) a solution of the polymer in a solvent 2, wherein solvents        1 and 2 are miscible;    -   (b) extruding is performed from the mixture obtained in (a); and    -   (c) a stretch ratio of at least 5 is applied below the melting        point of the polymer.

This embodiment is especially useful for making elongated products frompolymers that are best dissolved and spun from a solvent, which is not avery suited solvent for making a colloidal nanotubes dispersion.

Preferably, the method according to the invention uses polyvinyls, likepolyvinylalcohol, polyacrylonitril, or copolymers thereof; aliphaticpolyketones, like an alternating copolymer of ethylene and carbonmonoxide; and polyolefines, preferably of high molar mass, as thepolymer. Even more preferred are high molar mass polyolefines, likepolypropylene and polyethylene and their copolymers, because very strongfibres can be obtained via solution spinning. Most preferably, a highmolar mass polyethylene, like an ultra-high molar mass polyethylene(UH-PE) is used. Such polyethylenes have molar masses above about500,000 g/mol, more preferably above about 1,000,000 g/mol (mass orweight averaged molar mass, M_(W)). The polyethylene may contain minoramounts of one or more other alpha-olefins as a comonomer, such aspropylene, butylenes, pentene, hexane, 4-methylpentene, octene, and thelike. Preferably, the polyethylene is substantially linear, which isunderstood to mean that the polyethylene contains less than 1 side chainor branch per 100 carbon atoms, preferably less than 1 per 500, and morepreferably less than 1 per 1000. Whereas such high molar mass polymersmay be too viscous in the melt to allow a melt extruding or spinningprocess, with a solution spinning process, more specifically with a gelspinning process, elongated products like polyethylene fibres of highstrength and modulus can be produced. Stretching the product below T_(m)during solution, gel and/or solid-state stretching results in a markedincrease in tensile properties.

In one embodiment of the method according to the invention a colloidaldispersion is made by mechanically dispersing nanotubes in a ‘goodsolvent’ for nanotubes, optionally with sonication; that is withultra-sonic vibration. Various hydrocarbons are mentioned as suitablesolvents in WO 9839250 A1. Preferably, the solvent (or solvent 1 in step(a1)) is selected from the group of halogenated hydrocarbons, morepreferably from chlorinated hydrocarbons. Use of these solvents resultsin smaller ropes of nanotubes. Suitable examples include chlorinatedaliphatic hydrocarbons and chlorinated aromatic hydrocarbons. Very smallaggregates and some individual dispersion may result when using solventslike 1,2-dichloroethane and 1,2-dichlorobenzene. It has further beenobserved that dispersion is better if a low concentration of nanotubesin solvent 1 is used. Too low a concentration, however, is not practicaland might cause problems in subsequent steps of the method according tothe invention. A suitable concentration range is therefore 0.1-10 mass %nanotubes in solvent 1, preferably 0.5-5 mass %, more preferably 1-3mass %. The concentration and amount of (a1) is preferably chosen such,that after combining with (a2) the mixture contains about 0.5-20 mass %of nanotubes based on the polymer, preferably about 1-15 mass %, andeven more preferably about 2-10 mass %; this also being theconcentration of nanotubes in the finally obtained fibre.

In another preferred embodiment a dispersion aid, like a surfactant isadded to (a1) as other component, the advantage being an even betterdispersion. Optionally, sonication may be used. Preferably a non-ionicsurfactant is used, like an ester- or amide-derivative of a long chaincarboxylic acid, like a fatty acid, or a block copolymer containing twoblocks of different character. Typical examples of the latter arecompounds containing an aliphatic polyether segment, for example basedon an alkylene oxide, combined with a more apolar segment. Suchcompounds are also used in other application areas, such as indispersing colorants in a polymer matrix, and are known to the personskilled in the art. Another example of a suitable dispersion aid is ahighly branched oligomer or copolymer containing both polar and apolargroups, for example a polyesteramide copolymer. With such a highlybranched oligomer as dispersion aid, very finely dispersed nanotubes canbe obtained.

Preferably, nanotubes are mixed with the dispersion aid as such, beforediluting with solvent 1. In view of the very high surface area ofnanotubes, a relatively large amount of dispersion aid proves to beuseful, that is amounts equalling or exceeding the mass of nanotubes maybe used. The advantage of using dispersion aids, is that also colloidaldispersion in more polar solvent can be prepared. An, advantageouseffect of using a surfactant on dispersing nanotubes was alsodemonstrated in Chem. Mater. 2000, 12, 1049-1052, in making a thermosetepoxy composite from an acetone solution, but this publication is silenton using nanotubes in fibre spinning.

In another embodiment of the method according to the invention, acertain amount of the polymer is already added to (a1) as othercomponent. This may be done before, during or after initially dispersingthe nanotubes. It is also possible to dissolve the polymer in a separateamount of solvent 1, and then combine the nanotubes dispersion andpolymer solution. The advantage of adding a certain amount of thepolymer in this stage is that the polymer helps preventingre-aggregation of nanotubes into non-dispersed particles. The polymerconcentration in (a1) is preferably relatively low, for example lessthan 5 mass %, preferably less than 2.5 mass % based on (a1), so thatthe viscosity of the mixture remains relatively low to ensure bettermixing and/or dispersing.

In a further embodiment of the method according to the invention, thedispersion (a1) can be first prepared with a low concentration ofcomponents, but can be concentrated after a colloidal dispersion of thenanotubes is obtained. The advantage thereof is, that a possiblenegative effect of solvent 1 on producing an elongated product from thepolymer solution after combining (a1) and (a2) is reduced or prevented,while still an optimum dispersion can be made. Such a negative effectmay result if solvent 1 would for example hamper solidification of afluid product of polymer solution into a solvent-containing gel product.Especially in case (a1) also contains some of the polymer,re-aggregation of nanotubes into aggregates during such a concentrationstep is prevented.

In still another embodiment of the method according to the invention,nanotubes that have been chemically modified are used in step (a). Suchmodification may have introduced functional groups at the end of thetube, which may be opened, or on the surface. These functional groupsaffect the surface properties of the nanotubes, and contribute to easierdispersion into individual nanotubes in a solvent. Such functionalgroups may contribute to the desired increase in strength of thecomposite elongated product. Chemical modification of SWNT is a.o.described in WO 98/39250 A1.

As already described above, solvent 1 is a ‘solvent’ for nanotubessolution processing of the polymer concerned. In case of highly polarpolymers like aromatic polyamides, polybenzoxazoles orpolybenzothiazoles solvent 2 will often comprise a highly concentratedstrong acid; solvent 1 is miscible and compatible therewith. For theother group of polymers indicated above, solvent 2 is generally anorganic solvent with a polar or apolar character, depending on thepolymer. Typical examples include N-methylpyrrolidone,dimethylacetamide, alcohols or glycols, and aliphatic or aromatichydrocarbons. Preferably, solvent (1) and solvent (2) are the same.

Polyolefines of high molar mass, especially UH-PE, as used in apreferred embodiment of the method according to the invention, are inmany solvents only soluble at higher temperatures and solutions obtainedcan solidify upon cooling into a gel-like mass, also referred to as gelproduct. This effect is advantageously used in the so-calledgel-processing or gel spinning of UH-PE solutions into high strengthelongated products, especially fibres. Suitable solvents as solvent 2for this process are aliphatic, cycloaliphatic and aromatic hydrocarbonswith boiling points of at least 100° C., preferably at least equal tothe extrusion or spinning temperature. The solvent may be removed fromthe spun fiber by evaporation or by extraction with another solvent thatis miscible with the spinning solvent and is a non-solvent for thepolymer. In the first case, the boiling temperature of the solvent ispreferably not so high that evaporation from the product spun becomesvery difficult. Typical examples include octane, nonane, decane orisomers thereof and other linear or branched hydrocarbons, likeparafines, petroleum fractions, toluenes or xylenes, naphthalene, orhydrogenated derivatives thereof, such as tetraline, decaline, but alsohalogenated hydrocarbons. A suitable combination of solvent 1 andsolvent 2 is dichlorobenzene and decaline. The concentration of thepolymer in solvent 2 is chosen such that (a2) has a suitable viscosityfor processing this solution into elongated products like fibres in step(b), and will be dependent on the solvent, the molar mass and type ofpolymer, as well as on processing conditions, like temperatures andshear rates. Suitable concentration ranges may vary from 1 to 50 mass %,for UH-PE a typical range is 2-30 mass %, preferably 5-15 mass %.

In step (b) of the method according to the invention said polymersolution containing dispersed nanotubes is spun into elongated products,like fibres, through a spinneret comprising at least one orifice orhole. The dimensions and geometry of the orifice may vary substantially,and can be optimised by the skilled person depending on the type ofpolymer and solvent used. Upon leaving the orifice the product may stillbe in a fluid state (solution product), but show enough strength towithstand some drawing before the product solidifies. Generally, thesolution product is extruded into air before it is cooled in e.g. aliquid bath, during which phase the product can be highly stretched. Thesolution stretch ratio, including possible stretching in the orifice andin the air-gap, normally referred to as solution draw ratio or draw downratio, may vary within wide ranges; from 1 of up to several hundreds,and stretching can be performed above or below T_(m), depending on thetype of polymer. For polymers with relatively flexible molecules, likepolyolefins, the solution stretch ratio may be relatively low, whereasrigid chain polymers are extensively stretched in this phase. Thesolution product may be cooled by a flow of air, or by quenching in aliquid, being a non-solvent for the polymer. If this liquid is misciblewith solvent 1 and/or 2, the solvent can be extracted from the fibre.The liquid is generally also a non-solvent for the nanotubes, so thatthese remain in the polymer phase. If the quenching liquid is notmiscible with solvent 2, it merely functions as an alternative toair-cooling. In this case a solidified product is obtained that stillcontains solvent 2. This solvent-containing product is generallyreferred to as being in a gel-state and called a gel product. Part ofthe solvent may be removed by extraction or evaporation. During suchremoval, the temperature may be increased somewhat, but should not be sohigh that the polymer would re-dissolve, and will normally be belowT_(m). This gel product may again be stretched, typical gel stretchratios may vary from 1 to about 100 or even more, depending on the typeof polymer and stretch ratios applied in the other stages (solution andsolid-state). Subsequently, remaining solvents can be removed from thestretched product by extraction or evaporation, again taking care not todisrupt polymer crystallinity by increasing the temperature too much,that is not above the temperature at which the gel changes back to asolution and not above T_(m), preferably at least several degrees belowT_(m), until the fibre is substantially free of solvent. It should berealized, that T_(m) of the polymer can increase upon increasingmolecular orientation during stretching. Stretching and removal ofsolvent can also take place simultaneously.

After removal of solvent, the product can subsequently be furtherstretched in the solid state below T_(m). The solid-state stretch ratiothat can be applied is again dependent on the type of polymer andstretch ratios applied in the other stages (solution and gelstretching). In general it can vary from 1 up to about 100 or even more.Preferably, solid-state stretching is performed at elevated temperature,up to slightly below the crystalline melting point T_(m) of the polymerin the product. Solid-state stretching may also take place in more thanone step; for example at different, increasing temperatures. This mayresult in a higher maximum stretch ratio and in better mechanicalproperties of the fibre.

In the method according to the invention the stretch ratio that isapplied to the product below the melting point of the polymer, is atleast 5. This stretch ratio is the total or overall stretch ratio and iscalculated as the multiplication of the stretch ratios applied to theproduct below the melting point of the polymer in the various possiblestages of the method; which can include the solution stretch ratio, thegel stretch ratio and/or the solid-state stretch ratio.

Preferably, this total stretch ratio applied below T_(m) is at least 10,more preferably at least 20, even more preferably at least 50, stillmore preferably at least 100, even more preferably at least 200. Theadvantage of applying a higher stretch ratio below T_(m) is a betterorientation of both polymer molecules and nanotubes, resulting in highertensile strength.

The invention further relates to high strength elongated products,preferably fibres, containing nanotubes obtainable by the methodaccording to the invention.

The invention especially relates to high strength aromatic polyamide andpolyolefin elongated products, preferably fibres, containing nanotubes.More specifically, the invention concerns such fibres having a tensilestrength of higher than 3.0 GPa, preferably higher than 3.5 GPa, morepreferably higher than 4.0 GPa, still more preferably higher than 4.5GPa, even more preferably higher than 5.0 GPa, still more preferablyhigher than 5.5 GPa, and most preferably higher than 6.0 GPa.

Preferably such high strength polyolefin fibres are made from acomposition comprising ultra high molecular weight polyethylene with amass average molecular weight of more than 500.000 g/mol and nanotubes.Such polyolefin fibres may be produced on an industrial scale asmulti-filament yarns using the method according to the invention.Polyethylene fibres of such high strength have been mentioned before inliterature, but only for a monofilament made on laboratory scale and notcontaining dispersed nanotubes.

The invention also relates to a process for making composite articleswherein high strength elongated products, like fibres, containingnanotubes obtainable by the method according to the invention are used.The advantage of this process is that a lower amount of fibres can beused for making an article of certain properties, or articles of highermechanical strength can be made. Examples of such composite articlesinclude ropes, nets, cables, and anti-ballistic composites like panelsor protective clothing. Especially for making anti-ballistic compositesof lower weight, that still show the required protective performance,fibres containing nanotubes and having improved strength areadvantageous.

1. Method of producing a high strength and high modulus elongatedproduct comprising the steps of (a) making a composition comprising asemi-crystalline polymer and nanotubes, (b) extruding said compositioninto an elongated product, and (c) stretching the product below themelting point of the polymer, wherein in step (a) the composition is acolloidal dispersion of nanotubes in a solution of the polymer. 2.Method according to claim 1, wherein the nanotubes are carbon nanotubes.3. Method according to claim 1, wherein the nanotubes are single-wallnanotubes.
 4. Method of producing a high strength and high moduluselongated product comprising the steps of (a) making a compositioncomprising a semi-crystalline polymer and nanotubes, (b) extruding saidcomposition into an elongated product, and (c) stretching the productbelow the melting point of the polymer, wherein in step (a) thecomposition is a colloidal dispersion of nanotubes in a solution of thepolymer and is obtained by mixing (a1) a colloidal dispersion ofnanotubes and optionally other components in a solvent 1; and (a2) asolution of the polymer in a solvent 2, wherein solvents 1 and 2 aremiscible, and wherein in step (c) a stretch ratio of at least 5 isapplied.
 5. Method according to claim 1, wherein the semicrystallinepolymer is at least one selected from the group consisting ofpolyamides, polyesters, polyketones, polyoxazoles, polyimidazoles,polyvinyls and polyolefins.
 6. Method according to claim 5, wherein thesemicrystalline polymer is a polyethylene of molar mass Mw above about500,000 g/mol.
 7. Method according to claim 4, wherein solvent 1 in (a1)is a halogenated hydrocarbon.
 8. Method according to claim 4, wherein atleast one other component in (a1) is used and comprises a dispersionaid.
 9. Method according to claim 8, wherein the dispersion aid is anon-ionic surfactant.
 10. Method according to claim 4, wherein at leastone other component in (a1) is used and comprises the polymer. 11.Method according to claim 4, wherein (a1) is first prepared with a lowconcentration of components, but is concentrated after a colloidaldispersion of the nanotubes is obtained.
 12. Method of producing a highstrength and high modulus elongated product comprising the steps of (a)making a composition comprising a semi-crystalline polymer andnanotubes, (b) extruding said composition into an elongated product, and(c) stretching the product below the melting point of the polymer,wherein in step (a) the composition is a colloidal dispersion ofnanotubes in a solution of the polymer and further comprising a stepwherein the product is stretched as a gel product below the meltingpoint of the polymer.
 13. Method according to claim 1, wherein theelongated product contains about 1-10 mass % of nanotubes based on thepolymer.
 14. Method of producing a high strength and high moduluselongated product comprising the steps of (a) making a compositioncomprising a semi-crystalline polymer and nanotubes, (b) extruding saidcomposition into an elongated product, and (c) stretching the productbelow the melting point of the polymer, wherein the stretch ratioapplied below the melting point of the polymer is at least
 10. 15. Fibrecontaining a semi-crystalline polymer and nanotubes, wherein the fibrehas a tensile strength of higher than 3.0 GPa, and wherein thesemi-crystalline polymer is selected from the group consisting ofpolyesters, polyketones, polyvinyls and polyolefins.
 16. A compositearticle comprising nanotube-containing fibre according to claim
 15. 17.Anti-ballistic composites comprising fibres according to claim
 15. 18.Method according to claim 4, wherein the semicrystalline polymer is atleast one selected from the group consisting of polyamides, polyesters,polyketones, polyoxazoles, polyimidazoles, polyvinyls and polyolefins.19. Method according to claim 4, further comprising a step wherein theproduct is stretched as a gel product below the melting point of thepolymer.
 20. Method according to claim 4, wherein the elongated productcontains about 1-10 mass % of nanotubes based on the polymer.
 21. Methodaccording to claim 4, wherein the stretch ratio applied below themelting point of the polymer is at least
 10. 22. Ultrahigh molecularweight polyethylene (UHMWPE) fibres containing nanotubes, wherein theUHMWPE fibres have a tensile strength of higher than 3.0 GPa.
 23. Acomposite article comprising the UHMWPE fibres according to claim 22.24. Anti-ballistic composites comprising the UHMWPE fibers according toclaim
 22. 25. Method according to claim 1, wherein the polymer is apolyethylene of molar mass Mw above about 1,000,000 g/mol.
 26. Fibrecontaining a semi-crystalline polymer and nanotubes, wherein the fibrehas a tensile strength of higher than 3.0 GPa, and wherein thesemi-crystalline polymer is a polyolefin.
 27. A composite articlecomprising nanotube-containing fibre according to claim
 26. 28.Anti-ballistic composites comprising fibres according to claim 26.